This invention relates generally to a method for forming a roller compacted concrete industrial floor slab, and more particularly to such a method for forming a roller compacted concrete monolithic, untopped, industrial floor slab as well as a roller compacted concrete industrial floor slab having a thin topping.
Roller compacted concrete (RCC) is concrete, but it is placed by nontraditional methods. This requires a drier or stiffer consistency. RCC can have a much broader range of material properties than conventionally placed concrete, it can use aggregates not meeting normal requirements, it can be placed at very high production rates, and it can be much less expensive.
By definition, RCC is concrete comprising a damp mixture of cement, sand, aggregate and water, having a consistency allowing it to be compacted with a heavy vibratory roller, for example, a ten-ton roller intended for asphalt and granular base. RCC is usually mixed in a continuous process rather than in batches, delivered with trucks or conveyors, spread in layers using a bulldozer, and given final compaction with a vibratory roller.
RCC has generally been used for applications such as dam construction, pavement and bridge deck construction requiring a thick topping, usually two inches, as an essential element to achieve the required strength and fatigue life of the exterior slabs.
Heretofore, RCC has not been developed for use as an industrial floor slab adapted to withstand hard tire and steel wheeled equipment in combination with fixed rack loads for slabs on grade, versus aircraft, trucks and mixed soft tired vehicles for highways and airports with no fixed loads in pavement applications. The critical gross loads for design are very different for industrial floor slabs compared to pavement applications.
The tolerances and service requirements for pavements are different from those typically specified for the type of slab on grade work according to the present invention. Even the method of measurement for tolerance is different. Also, the placing procedures and equipment used are very different for pavements compared to slabs on grade. Typical highway pavement equipment and finishing procedures are not available to practically place, finish, or provide the industrial floor slab of the invention.
RCC pavement technology has not been considered as suitable for industrial floor slabs where a much denser, flatter and easily cleaned surface is required. Types of loads supported on a floor slab are markedly different, and the pavement or dam construction RCC does not require the surface finish needed for an industrial floor slab compared to an RCC pavement which is normally formed with a skid resistant surface. Industrial floors also require a high ride quality in all directions as compared to pavements which require a ride quality in only the direction of traffic.
Industrial floor slabs, typically subjected to uneven loading, rack loading, and concentrated postloads, require different design considerations compared to that of pavements.
Joints in pavements typically use a relatively soft filler material, the main objective of which is to exclude debris accumulation. Floor slabs normally undergo less extreme critical variations and generally use a harder filler material in order to provide for load continuity across the joint. And, in some industrial floor slab applications, such as in freezers and the like, the floor slab is subjected to relatively large temperature fluctuations, such as between minus 20.degree. F. and plus 80.degree. F. or higher during cleaning cycles. Although the cycles are infrequent, the stresses to which the floor slab are subjected are significant. Further, floor slabs often require highly finished surfaces to reduce porosity and minimize chemical attack, especially in locations where food and food products are prepared.
Curing methods for floor slabs are also different from paving operations, as curing may require active removal of excess water and special ventilation when the floor slab is applied to interior applications.
U.S. Pat. No. 4,981,626 to Uchizaki relates to a method for forming a dense concrete surface layer on concrete placed by traditional methods. This prior art method does not relate to roller compacted concrete, or to improvements in RCC pavements structures to which the present invention relates.
As a first step according to the Uchizaki method, concrete having a water/cement ratio of 45% is placed on the ground and subjected to vibrations with a frequency of 100 Hz and an amplitude of 3 mm applied to the concrete surface by a vibrator immediately after placement. The concrete is left to stand for four hours. If the frequency and amplitude are less than 100 Hz and 1 mm, the vibrator necessary for forming an effective mortar layer becomes too large.
During the first step, coarse aggregate particles are allowed to sink into the interior of the slab due to the vibrations imparted by the vibrator, thereby forming a mortar layer.
The standing time is such that the water/cement ratio of the mortar surface becomes 15 to 20 percent, beyond which a dense layer ceases to be formed.
As a second step, an ultrasonic vibrator with a frequency of 19.5 kHz and an amplitude of 5 .mu. is applied to the mortar surface with a pressure of 0.05 kg/cm.sup.2, the ultrasonic vibrator being moved at a given velocity so as to scrape off the surface of the mortar layer. By scraping off the mortar surface during this second step using the ultrasonic vibrator, large surface irregularities are said to be removed and a smooth surface is said to be formed. A water-shielding layer forming a dense layer is said to be formed to prevent water from moving up from the interior of the concrete below the water-shielding layer to the surface at the time when the third and fourth steps are performed.
As a third step, a mortar layer is spread onto the surface of the scraped concrete and is fluidized by a high vibrating pressure.
As a fourth step, an ultrasonic vibrator is applied to the water-shielding layer of the mortar layer at a given pressure and is moved at a given velocity to allow the mortar layers to be integrated together to achieve a very dense layer having a thickness of 1 cm or thereabouts.
The surface finish achieved during the formation of a roller compacted concrete floor slab according to the invention is wholly unlike that of the dense concrete surface layer formed by Uchizaki on conventionally placed concrete.